The present invention relates generally to methods and apparatus for changing an input speed to an output speed. More particularly, the present invention relates to a method and apparatus for providing an infinitely variable output speed from a generally constant input speed.
Speed changing devices are employed in many types of equipment. In a simple transmission, for example, devices are often provided to give one or more discrete output speeds in relation to an input speed. In other equipment, it is necessary to have a wider variety of output speeds available. In such other equipment, the output speed often needs to vary continuously, or infinitely, over the desired speed range while only a constant speed is available as input.
One of the more common variable speed changing devices employs a fixed length V-belt and a pair of cooperating pulleys. The pulleys may have the ability to adjust the V diameter on which the belt operates in order to obtain a variable output speed. Typically, one such adjustable pulley mechanism is driven while another adjustable pulley mechanism is spring-loaded to maintain tension on the V-belt and to make the second adjustable pulley mechanism responsive to changes made in the first driven adjustable pulley mechanism.
A somewhat analogous speed changing device employs a variable V-drive in combination with another traction driven fixed-width drum. Sometimes a plurality of these drums are employed to increase the maximum power transmission capability. These devices occasionally use elements packaged in planetary movement arrangements with one device at the center and a multiplicity of encircling meshing elements having planetary movements.
Another class of variable speed drives can be characterized as the ball and disc type. In this class of drive mechanisms, the rotational axis for a ball element is usually at a substantially right angle to the rotational axis of a disc element. The ball element which has a surface of revolution is positioned so that when it is pressed against the rotating disc element, the ball element is driven by the disc. By moving the ball element along a radius of the disc element, a variable speed drive can be obtained from the ball element.
Another class of speed regulation employs purely inertial devices. Flywheel governors are common examples of inertial devices that have been used to control internal combustion engine speed under varying load conditions for many years.
Each of the various infinitely adjustable speed changing devices currently available have various problems and limitations. One common problem is the presence of residual slippage between traction elements. Such slippage is undesirable since it wastes energy, generates heat, promotes wear, and increases working clearances.
Another common problem is that many of the materials commonly used to fabricate components of variable speed devices are subject to rapid wear. As a result, the devices experience increased clearances with attendant noise, slippage and reduced efficiency. Wear also tends to create objectionable dirt and particles resulting from degradation of the materials.
Many of the available speed changing devices also exhibit poor power transmission capability for the spatial volume which they occupy. That is, a large and usually heavy transmission is needed to transmit modest power levels. As a result, to transmit large amounts of power, a physically large transmission is required, adding to the weight of the device.
Many of the available speed changing devices also fail to provide the ability to reverse the direction of output rotation while the input operates at a uniform speed in a constant direction. This capacity can be desirable for example in motorized vehicles where a constant speed input could be varied so as to provide both forward and reverse drive speeds.
Generally, the design characteristics of the known variable speed transmissions do not permit the rate of speed variation to be controlled in the design process. Without the ability to regulate speed change variations during the design, the response of the transmission to a control input cannot be selected by the designer to meet his specific design problem.
Most known transmission systems are also critically dependent upon lubrication, cleanliness or transmission fluids in order to provide and maintain their speed change capability. In many desirable applications of variable speed transmissions, it is extremely difficult, if not impossible, to lubricate or maintain cleanliness.
Another deficiency of most known speed change devices is the necessity for a clutch to permit the output speed or angular velocity to go to zero (i.e. stop) while the power supply is still operating. Clutches clearly introduce additional complexity into a system as well as expense, bulk and weight. In a similar vein, must known devices which do permit a zero output speed lack sufficient traction at that speed to be useful. Traction near zero is necessary in order to create useful starting movement without slippage in the transmission device.
Still further, most known devices are unable to run at the maximum speeds that could be advantageous for many applications. This inability to run at high speed is often a result of the fact that locally generated heat can devulcanize rubber, soften heat-treated materials, generate noise, and cause vibrations as well as other undesirable effects.
The control of known variable speed devices has also been a problem. More particularly, most devices do not have a sufficiently sensitive control that can give small changes in the output speed settings. In many useful applications for variable speed devices, such sensitivity to small changes in response are highly desirable.
From the foregoing, it will be clear that the need continues to exist for a speed changing device which overcomes problems of the type discussed.